HYDROGENATION. A 8 /. SOLID 8 /. 8 ;. AT. Au/Al2O3 âas preparedâ as prepared. Au/TiO2 âas preparedâ. Au/Al2O3 reduced. Au/TiO2 reduced. (a) as prepared.
3UPPORTEDGOLD CATALYSTSFORSELECTIVE HYDROGENATIONOF BUTADIENEINTHE PRESENCEOFAN EXCESSOFALKENES !NTOINE(UGON ,AURENT$ELANNOY #ATHERINE,OUIS
,ABORATOIREDE2mACTIVITmDE3URFACE 5-2#.23 5NIVERSITm0IERREET-ARIE#URIE 0ARIS PLACE *USSIEU 0ARIS #EDEX &RANCE
CORRESPONDINGAUTHOR E MAILCATHERINELOUIS UPMCFR
!BSTRACT 3UPPORTEDGOLDCATALYSTSWEREINVESTIGATEDINTHE SELECTIVEGASPHASEHYDROGENATIONOF BUTADIENEIN ANEXCESSOFPROPENEBUTADIENE PROPENE ANDHYDROGEN INORDERTOSIMULATETHEPROCESS REQUIREDFORTHEPURI½CATIONOFINDUSTRIALALKENES STREAMSTOPREVENTPOISONINGOFTHEPOLYMERISATION CATALYSTSUSEDFORPOLYALKENEPRODUCTION'OLD CATALYSTSCONTAININGSMALLGOLDPARTICLESBETWEEN TONMINAVERAGE ARELESSACTIVETHANCOMMERCIAL PALLADIUMCATALYSTS BUTTHEYAREMUCHMORESELECTIVE 5NDEROUREXPERIMENTALCONDITIONS OF BUTADIENECANBECONVERTEDAT^#INTO BUTENESWITH BUTENEASTHEMAINPRODUCT ANDWITH ONLYVERYSMALLAMOUNTOFALKANESFORMED^ PPM 4HEABSENCEORPRESENCEOFPROPENEDOESNOT DRASTICALLYMODIFYTHERATEOFHYDROGENATIONOF BUTADIENE 0ARAMETERSDIRECTLYRELATEDTOTHENATUREOFTHE GOLDCATALYSTSWEREALSOINVESTIGATED&ORAGIVEN PREPARATIONMETHODDEPOSITION PRECIPITATIONWITH UREA$05 GOLDPARTICLESIZEANDGOLDLOADING THENATUREOFTHEOXIDESUPPORTALUMINA TITANIA ZIRCONIA CERIA DOESNOTIN¾UENCETHEGOLDREACTIVITY 4HEVARIATIONSOFGOLDPARTICLESIZEANDGOLDLOADING DONOTINDUCECHANGESINTHE4/&EXPRESSEDPER SURFACEGOLDATOMS 4HEMETHODOFPREPARATION HASANIN¾UENCEWHENITLEAVESCHLORINEINTHE SAMPLESIMPREGNATIONINEXCESSOFSOLUTIONAND ANIONICADSORPTION )NSUCHACASE THEGOLDCATALYSTS ARELESSACTIVE
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+EYWORDS GOLD CERIA TITANIA ALUMINA ZIRCONIA REDUCIBILITY HYDROGENATION BUTADIENE PROPENE BUTENE $2)&43 402 4%- CATALYSIS
)NTRODUCTION ,IGHT ALKENES PRODUCED BY CATALYTIC CRACKING OF PETROLEUM CONTAIN SIGNI½CANT AMOUNTS OF ALKADIENES OR ALKYNES 4YPICALLY THE ETHYLENE CUTS CONTAIN TO OF ACETYLENE ANDTHEPROPENECUTSTOOFPROPYNEANDPROPADIENE "EFORE SUBSEQUENT PROCESSING THESE RAW STREAMS MUST BE PURI½ED&ORINSTANCE FORFURTHERPOLYMERISATIONPROCESSING THELEVELOFIMPURITYINALKADIENESORALKYNESMUSTBEASLOW ASPPM 4HEREFORE THESEMOLECULESMUSTBESELECTIVELY CONVERTED TO ALKENES WITHOUT FURTHER HYDROGENATION OF THE ALKENE STREAM 0ALLADIUM IS SO FAR REGARDED AS THE UNIQUE METAL WHICH HAS THE COMMERCIAL ABILITY TO SELECTIVELY HYDROGENATE ALKADIENES OR ALKYNES IN AN EXCESS OF ALKENES ANDITISUSEDININDUSTRYFORGAS ANDLIQUID PHASESELECTIVE HYDROGENATION(OWEVEROLIGOMERS³GREENOIL´ FORMDURING HYDROGENATION OVER SUPPORTED 0D CATALYST WHICH SHORTENS THERECYCLETIMEANDLIFEOFTHEINDUSTRIALCATALYST-OREOVER IF PALLADIUM IS HIGHLY SELECTIVE WHEN THE CONCENTRATION OF IMPURITIES IS STILL HIGH IN CONTRAST FOR ULTIMATE PURI½CATION ANDELIMINATIONOFTRACESOFALKADIENESORALKYNES IE ATHIGH CONVERSION ALKENESSTARTTOBEHYDROGENATED ANDPALLADIUM CATALYSTSARENOTSELECTIVEENOUGH4OLIMITTHESEPROBLEMS PROMOTERSSUCHAS!G #O #U #R ALKALIMETALS LEADACETATE ANDMETALOXIDESAREADDEDTO0DCATALYSTS&ORINSTANCE THE ADDITION OF A GROUP ) " METAL TO 0D CATALYSTS INCREASES THE SELECTIVITY OF ACETYLENE HYDROGENATION TO ETHYLENE REDUCES THE YIELD OF ³GREEN OIL´ AND IMPROVES THE PROPERTIES OF TRADITIONAL0DCATALYSTS /N THE OTHER HAND THE FEW STUDIES PERFORMED OVER SUPPORTEDGOLDCATALYSTSSHOWEDTHATGOLDWASHIGHLYEF½CIENT FOR SELECTIVELY HYDROGENATING ALKADIENES OR ALKYNES AT HIGH CONVERSION EVENTHOUGHGOLDWASNOTASACTIVEASPALLADIUM 4HE½RSTSTUDIESWEREREPORTEDBY"ONDAND7ELLSINTHE SEVENTIES IE ALMOSTYEARSBEFORETHEDISCOVERYBY 0ROF(ARUTAANDHISTEAMTHATGOLDCATALYSTSWEREAMAZINGLY ACTIVE IN #/ OXIDATION AT ROOM TEMPERATURE OR BELOW 24 PROVIDINGTHATSMALLGOLDPARTICLESCOULDBEPREPARED(ENCE THE ½RST STUDIES PUBLISHED WERE PERFORMED WITH CATALYSTS CONTAININGLARGEGOLDPARTICLESUPTONM )NSPITEOFTHAT "OND AND 7ELLS REPORTED THAT GOLD SUPPORTED ON ALUMINA AND BOEHMITE HYDRATED ALUMINA WAS ABLE TO SELECTIVELY HYDROGENATE BUTADIENE INTO BUTENES WITHOUT BUTANE FORMATIONBETWEENAND#-ORERECENTLY /KUMURA AND (ARUTA REPORTED A STUDY PERFORMED ON A SERIES OF GOLDCATALYSTSSUPPORTEDONVARIOUSSUPPORTSALUMINA TITANIA AND SILICA PREPARED BY DIFFERENT METHODS AND CONTAINING DIFFERENTAVERAGEGOLDPARTICLESIZESFROMTONM !LL THECATALYSTSWEREABLETOSELECTIVELYHYDROGENATEBUTADIENE INTOBUTENESWITHSELECTIVITY ANDTHEREACTIONOF BUTADIENEHYDROGENATIONOVER!UCATALYSTSWASFOUNDALMOST
INSENSITIVETOTHESIZEOFTHEGOLDPARTICLESANDTHENATUREOF THEOXIDESUPPORTS 3ELECTIVE HYDROGENATION OF ACETYLENE AND ETHYLENE WERE ALSO PERFORMED OVER GOLD CATALYSTS CONTAINING SMALL GOLD PARTICLES NM IN !U!L/ PREPARED BY DEPOSITION PRECIPITATION "ELOW # IN BATCH REACTOR GOLD WAS ABLE TO HYDROGENATE ACETYLENE INTO ETHYLENE WITH SELECTIVITY 4HE SAME TYPE OF RESULTS WAS THEN REPORTED FOR !U4I/ IN A CONTINUOUS ¾OW REACTOR 4HE CATALYST CONTAININGLARGEGOLDPARTICLESNM IMPREGNATIONMETHOD SHOWED MUCH LOWER ACTIVITY THAN THAT CONTAINING SMALL PARTICLES NM GRAFTING OF A GOLD PHOSPHINE PRECURSOR WHICHSHOWEDCONVERSIONAT#WITHASELECTIVITY HIGHER THAN ! PAPER ON SELECTIVE HYDROGENATION OF PROPYNE WAS ALSO PUBLISHED SHOWING AGAIN EXCELLENT SELECTIVITIESWITH!U4I/D!U NM AND!U&E/CATALYSTS D!U NM /NLY ONE STUDY WAS PERFORMED IN CONDITIONS CLOSER TO THOSEOFPURI½CATION4HISWASTHEHYDROGENATIONOFPROPYNE INPRESENCEOFPROPENEPROPYNEPROPENE(RATIOSOF INACONTINUOUS¾OWREACTOROVERA!U#E/CATALYSTPREPARED BY DEPOSITION PRECIPITATION D!U NM 0EREZ 2AMIREZ ETALOBSERVEDHIGHSELECTIVITYTOPROPENEAT# EVEN AT HIGH CONVERSION 4HE PRESENCE OF ADDITIONAL PROPENE LED TO A SLIGHTLY HIGHER SELECTIVITY BUT ALSO TO A SLIGHTLYLOWERCONVERSION 4HEGOALOFTHEPRESENTSTUDYWASTOEXPLORETHEPROPERTIES OFGOLDCATALYSTSINTHEREACTIONOFSELECTIVEHYDROGENATIONOF AN ALKADIENE IN THE PRESENCE OF AN EXCESS OF ALKENES IN CONDITIONSCLOSETOTHEREALCONDITIONSOFPURI½CATION IE WITH ANALKENEALKADIENERATIOOF)NTHESTUDYOF0EREZ 2AMIREZ ETAL REPORTEDABOVE THEPROPENEPROPYNERATIOWASEQUAL TO!MONGTHEMODELREACTIONSOFSELECTIVEHYDROGENATIONOF ALKYNES AND ALKADIENES IN ALKENES WE CHOSE THAT OF BUTADIENE IETHEISSUEOFTHEPURI½CATIONOFA#CUT BECAUSE IT GIVES FOUR DIFFERENT PRODUCTS THREE BUTENES AND BUTANE WITH BUTENEASTHEMOSTDESIRABLEPRODUCT ANDTHEREFORE ALLOWSTHESTUDYOFBOTHACTIVITYANDSELECTIVITYISSUES)NORDER TOBEABLETOEASILYDISTINGUISHTHEALKANEARISINGFROMTHETOTAL HYDROGENATION OF BUTADIENE FROM THAT ARISING FROM THE HYDROGENATIONOFTHEALKENEINEXCESS WECHOSETOSTUDYTHE REACTION OF SELECTIVE HYDROGENATION OF BUTADIENE IN AN EXCESSOFPROPENE4HECHOICEWASBASEDONTHEHYPOTHESIS THATTHEREACTIVITYOFPROPENEWASTHESAMEASTHATOFBUTENES THISHYPOTHESISWASAPOSTERIORIEXPERIMENTALLYJUSTI½EDBYOUR RESULTS)NTHEPRESENTPAPER PARAMETERSDIRECTLYRELATEDTOTHE NATURE OF THE CATALYSTS NATURE OF THE SUPPORT GOLD PARTICLE SIZE GOLDLOADING METHODOFPREPARATION WEREINVESTIGATED AS WELL AS PARAMETERS ARISING FROM THE REACTION MIXTURE REACTANTCONCENTRATIONS
%XPERIMENTAL !#ATALYSTPREPARATION 4ITANIA0 $EGUSSA MG !NATASE 2UTILE
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CERIA(3! 2HODIA MG ALUMINA!LU#$EGUSSA MG D TYPE AND ZIRCONIA 2HODIA MG WERE USED AS SUPPORTS AND (!U#L (/ !CROS #HEMICALS AS GOLD PRECURSOR"EFOREUSE #E/AND:R/WERECALCINEDUNDERAIR AT# 4HECATALYSTSWEREPREPAREDBYTHREEDIFFERENTMETHODS DEPOSITION PRECIPITATION WITH UREA $05 AS DESCRIBED PREVIOUSLY IMPREGNATIONINEXCESSOFSOLUTION)% AND ANIONIC ADSORPTION !! &OR EACH PREPARATION G OF SUPPORT AND MG OF (!U#L (/ WERE USED IN ORDER TO ACHIEVEANOMINALGOLDLOADINGOFWT 4HE CATALYSTS WERE PREPARED BY DEPOSITION PRECIPITATION WITHUREA$05 ASDESCRIBEDPREVIOUSLY USING4I/ #E/ !L/ AND :R/ AS SUPPORTS ! M, SOLUTION CONTAINING(!U#L - GOFUREACUREA ^XC!U ANDTHESUPPORTG WASPREPARED STIRREDAT#FORH INADARK CLOSEDREACTOR)TISWORTHNOTINGTHAT ASUREAISA POTENTIAL NITROGEN CONTAINING LIGAND FOR GOLD SOME CARE MUSTBEUSEDREGARDINGTHEPOSSIBLEFORMATIONOFFULMINATING GOLD 4HE SOLID WAS SEPARATED BY CENTRIFUGATION WASHEDFOURTIMESWITHDEIONISEDWATERWITHCENTRIFUGATION BETWEENEACHWASHING !FTERTHETHIRDWASHING AFEWDROPS OFSILVERNITRATEWEREADDEDTOTHEWASHINGSOLUTION ANDDID NOT SHOW ANY !G#L PRECIPITATION 4HE SAMPLES WERE THEN DRIEDUNDERVACUUMAT24FORH RESULTINGIN±AS PREPARED² SAMPLES &OR COMPARISON ONE !U!L/ SAMPLE WAS KEPT UNWASHED !U!L/SAMPLESWEREPREPAREDBYIMPREGNATIONINEXCESS OF SOLUTION )% G OF SUPPORT WERE WETTED WITH M, OF WATER 4HEN A M, SOLUTION OF (!U#L (/ MG WERE ADDED DROP BY DROP UNDER VIGOROUS STIRRING THENCONTINUOUSLYMIXEDFORANADDITIONALHOURINTHEDARK 4HENTHEMIXTUREWASDRIEDWITHAROTAVAPORAT#UNDER VACUUMFORONEHOUR !U!L/ SAMPLES WERE PREPARED BY ANIONIC ADSORPTION !! !M,AQUEOUSSOLUTIONCONTAININGGOFSUPPORT WASHEATEDTO#4HEN AM,SOLUTIONOF(!U#L (/ MG WERE ADDED DROP BY DROP UNDER VIGOROUS STIRRING THENCONTINUOUSLYMIXEDFORANADDITIONALHOURINTHEDARK 4HESOLIDWASSEPARATEDBYCENTRIFUGATION WASHEDFOURTIMES ANDDRIEDTHESAMEWAYASTHE$05SAMPLES !FTER DRYING ALL THE SAMPLES WERE STORED AT 24 UNDER VACUUMINADESICCATOR AWAYFROMLIGHTINORDERTOPREVENT ANY UNCONTROLLED REDUCTION OF GOLD 4HE COLOUR OF THE CATALYSTS DEPENDED ON BOTH THE NATURE OF THE SUPPORT ORANGE WITH ALUMINA YELLOW WITH CERIA LIKE CERIA AND WHITE FOR ZIRCONIA AND TITANIA FOR $05 SAMPLES AND THE PREPARATION METHOD WITH ALUMINA ORANGE BY $05 AND YELLOWFOR)%AND!! "EFORE CHARACTERISATION AND REACTION THE GOLD CATALYSTS WERE REDUCED UNDER ( AT # M,MIN #MIN FROM 24 TO # THEN FOR H AT # )N SOME CASES THERMALTREATMENTWASPERFORMEDATHIGHERTEMPERATUREOR UNDERAIR5PONREDUCTION THECOLOUROFTHESAMPLESCHANGES DEEPVIOLETFORTITANIA PINKPURPLEFORALUMINA BLACK BROWN FORCERIAANDPURPLEFORZIRCONIA
"4ECHNIQUESOFCHARACTERISATION #HEMICALANALYSESOF!U #LANDMETALCATIONOFTHESUPPORT WEREPERFORMEDBYINDUCTIVELYCOUPLEDPLASMAATOMEMISSION SPECTROSCOPY AT THE #.23 #ENTER OF #HEMICAL !NALYSIS 6ERNAISON &RANCE 4HE !U WEIGHT LOADING OF THE SAMPLES WASEXPRESSEDINGRAMOF!UPERGRAMOFSAMPLEWT!U ;M!UM!U MSUPPORT =X 4HEDRIEDSAMPLESMG WEREREDUCEDBYTEMPERATURE PROGRAMMED REDUCTION 402 IN A QUARTZ GAS ¾OW REACTOR FROM ROOM TEMPERATURE TO # WITH A HEATING RATE OF #MIN UNDERASTREAMOFVV(INARGONTOTAL¾OW RATE M,MIN ATATMOSPHERICPRESSURE4HEAMOUNTOF THE HYDROGEN CONSUMED WAS MEASURED WITH A THERMAL CONDUCTIVITYDETECTOR 4%- ANALYSIS WAS PERFORMED USING A *%/, *%- #8 )) MICROSCOPE OPERATING AT K6 'OLD PARTICLE SIZE MEASUREMENT WAS PERFORMED USING )4%- SOFTWARE ON DIGITIZED MICROGRAPHS .OTE THAT PARTICLES WERE MEASURED ONEBYONEANDNOTAUTOMATICALLY4HELIMITOFSIZEDETECTION WASABOUTNM BUTITWASEASIERTOMEASUREGOLDPARTICLES ON TITANIA THAN ON ALUMINA )T WAS NOT POSSIBLE TO MEASURE THEMONCERIABECAUSEOFTHETOOLOWCONTRASTBETWEENCERIA ANDGOLDPARTICLESDUETOTHEHIGHATOMICNUMBEROF#EAND THEHIGHSURFACEAREAOFCERIA 4HEAVERAGEMETALPARTICLE SIZESD!UWEREDETERMINEDFROMTHEMEASUREMENTOFATLEAST PARTICLES D!U WAS CALCULATED USING THE FOLLOWING FORMULAESD!U NIDINIDIVOLUMICMEAN ANDD!U 3NIDI 3NIARITHMETICMEAN WHERENIISTHENUMBEROFPARTICLESOF DIAMETERDI 82$ ANALYSIS WAS CARRIED OUT WITH A 3IEMENS $ DIFFRACTOMETERWITH#U+ARADIATION )NFRAREDSPECTROSCOPYWASPERFORMEDWITHAN)&36"RUKER SPECTROMETERUSINGA$2)&43CELLCOLLECTORFROM3PECTRATECH 4HE SAMPLE COMPARTMENT OF THE CELL WAS ½LLED WITH THE AS PREPARED GOLD SAMPLE ^ MG WHICH WAS REDUCED IN SITU FROMROOMTEMPERATURETO# WITHAHEATINGRATEOF# MIN UNDERASTREAMOFVV(INARGONTOTAL¾OWRATE M,MIN THENFORMINAT#4HECELLWASCOOLEDTO24 THEN PURGED WITH (E BEFORE INTRODUCTION OF A MIXTURE CONTAINING OF VV #/ IN (E ! REFERENCE SPECTRUM WAS RECORDED IN (E AND THE INTENSITY OF THE SPECTRUM IN #/(E ATMOSPHEREWASEXPRESSEDAS,OG)#/)REF ##ATALYTICREACTION 4HEHYDROGENATIONREACTIONWASCARRIEDOUTWITHMGOF CATALYST SIEVE FRACTION M IN A PLUG ¾OW MICROREACTOR IN PYREX MM OF INTERNAL DIAMETER %XCEPT WHENSPECI½CALLYMENTIONED THECATALYSTSWEREACTIVATEDIN SITU UNDERPURE(M,MIN FROM24TO## MIN ANDKEPTABOUTMINAT#4HEN THECATALYSTS WERE COOLED TO ROOM TEMPERATURE UNDER PURE ( AND THE REACTIONMIXTURECONSISTINGOFBUTADIENE PROPENE AND HYDROGEN WAS INTRODUCED WITH A ¾OW RATE OF M,MIN .40 CONDITIONS WHICH CORRESPONDS TO A SPACE VELOCITYOFM,G H '(36 H 4HECATALYSTS WEREHEATEDUNDERTHISGASMIXTUREATARATEOF#MIN UP
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TO # 'AS ANALYSIS AT THE OUTLET OF THE REACTOR WAS PERFORMED EVERY MIN IE EVERY # BETWEEN AND #)TWASCHECKEDTHATWITHTHESLOWHEATINGRATECHOSEN THE REACTION RATE WAS AT THE EQUILIBRIUM AT LEAST AT LOW TEMPERATURESSINCEDEACTIVATIONOCCURSATHIGHERTEMPERATURE 7HEN#WASREACHED THEREACTORWASGRADUALLYCOOLED AND OTHER MEASUREMENTS WERE PERFORMED AT DECREASING TEMPERATURE AND # TO EVALUATEPOSSIBLEDEACTIVATIONOFTHECATALYSTS4HEANALYSISOF REACTION PRODUCTS WAS EFFECTED BY GAS CHROMATOGRAPHY 0ERICHROM02 &)$DETECTOR USINGAMCOLUMN INCH ½LLEDWITHSEBACONITRILE#HROMOSORB0!7 -ESH 2ETENTIONTIMESANDSENSITIVITYFACTORSFORTHEREACTANTS AND PRODUCTS WERE CALIBRATED USING SEVERAL GAS MIXTURES 3OFTWARE 7INILAB WAS USED FOR DATA ACQUISITION AND EXTRACTION OF THE CONCENTRATIONS OF THE DIFFERENT GASES DETECTED 4ITANIA AND ALUMINA ALONE DID NOT SHOW ACTIVITY ONLY PPM OF BUTADIENE BEING HYDROGENATED AT # 4ESTS WERE ALSO MADE TO CHECK THAT UNDER THE CATALYTIC CONDITIONS DESCRIBED AND AT LOW CONVERSION INTERNAL AND EXTERNALDIFFUSIONLIMITATIONSCOULDBENEGLECTED.UMEROUS TESTSOFREPEATABILITYANDREPRODUCIBILITYWEREPERFORMEDTO VALIDATETHECONDITIONSOFREACTION 4HE ACTIVITIES OF THE CATALYSTS EXPRESSED IN MOLS GMETAL WERECOMPAREDAT#3INCEATTHISTEMPERATURE ACTIVITYWAS VERYLOW ACTIVITYWASCALCULATEDFROMTHEAPPARENTACTIVATION ENERGY MEASURED FROM THE !RRHENIUS PLOT LNACTIVITY VERSUS44/&EXPRESSEDPERSURFACEGOLDATOMWASESTIMATED AS FOLLOWS 4/& ACTIVITY#$-!U 4HE DISPERSION $ WAS DEDUCEDFROMTHEVOLUMICAVERAGEGOLDPARTICLEDAV MEASURED BY 4%- AND PLOTS OF THE DISPERSION VERSUS AVERAGE PLATINUM PARTICLESIZE
2ESULTS !#ATALYSTCHARACTERISATION 4HE GOLD LOADINGS AND AVERAGE GOLD PARTICLE SIZE OF THE SAMPLES REDUCED AT # ARE REPORTED IN 4ABLES 4HE RESULTS SHOW THAT ALL THE SAMPLES CONTAIN THE EXPECTED !ULOADINGWT ANDTHATTHECHLORINECONTENTINTHE$05 SAMPLESISALWAYSBELOWTHEDETECTIONLIMITOFMEASUREMENT !SEXPECTEDTHESAMPLESPREPAREDBYIMPREGNATIONINEXCESS OFSOLUTION)% ANDANIONICADSORPTION!! CONTAINAHIGHER AMOUNTOFCHLORINE !FORMER8!&3STUDYSHOWEDTHATGOLDONCERIA ALUMINA TITANIA PREPARED BY DEPOSITION PRECIPITATION WITH UREA WAS FULLYREDUCEDINTOMETALLICGOLDAFTERREDUCTIONUNDER(AT # WITHNODETECTABLETRACESOF!U)))OR!U)4HE402 PRO½LES REPORTED IN &IGURE CON½RM THAT GOLD IS REDUCED BELOW # 4HEY ALSO SHOW THAT THE REDUCIBILITY OF GOLD DEPENDSONTHENATUREOFTHESUPPORT INAGREEMENTWITHTHE SAMEFORMERSTUDY ANDALSOONTHEPREPARATIONMETHOD 4HE TEMPERATURES CORRESPONDING TO THE MAXIMUM OF THE REDUCTIONPEAKSWASAROUND#FOR!U4I/ #FOR!U #E/ # FOR !U:R/ AND # FOR !U!L/ $05
4ABLE 'OLDCATALYSTSPREPAREDBY$05ONDIFFERENTSUPPORTSGOLDANDCHLORINECONTENTS GOLDPARTICLESIZEAFTERREDUCTIONAT#IN( ACTIVITYAND4/& AT#
,OADINGWT !U #L
#ATALYSTS
!VERAGEGOLDPARTICLESIZENM !RITHMETIC 6OLUMIC MEAN
MEAN
!CTIVITYAT# MOLS G!U
4/&AT# S
!U4I/$05
!U!L/$05
!U:R/$05
!U#E/$05
STANDARDDEVIATION 4ABLE !U4I/AND!U!L/PREPAREDBY$05ATVARIOUSGOLDLOADINGSGOLDANDCHLORINECONTENTS GOLDPARTICLESIZEAFTERREDUCTIONAT#IN( ACTIVITYAND 4/&AT#
,OADINGWT !U #L
#ATALYSTS
!VERAGEGOLDPARTICLESIZENM !RITHMETIC 6OLUMIC MEAN
MEAN
!CTIVITYAT# MOLS G!U
4/&AT# S
!U!L/$05WT
!U!L/$05WT
!U!L/$05WT
!U4I/$05WT
!U4I/$05WT
STANDARDDEVIATION 4ABLE !U4I/AND!U!L/PREPAREDBY$05GOLDANDCHLORINECONTENTS GOLDPARTICLESIZEAFTERDIFFERENTTHERMALTREATMENTS ACTIVITYAND4/&FOR HYDROGENATIONAT#
#ATALYSTS
,OADINGWT !CTIVATION !U #L 'AS 4EMP#
!U4I/$05
!IR
!U4I/$05
!U4I/$05
!U4I/$05
!VERAGEGOLD PARTICLESIZENM !CTIVITYAT# !RITHMETIC 6OLUMIC MOLS G!U
4/&AT# S
MEAN
MEAN
!IR
!IR
(
!U4I/$05
(
!U4I/$05
(
!U!L/$05BATCH
(
!U!L/$05BATCH
(
!U!L/$05BATCH
(
!U!L/$05BATCH
(
STANDARDDEVIATION CATALYSTS )TISWORTHNOTINGTHATTHEHYDROGENCONSUMPTION FORTHE!U#E/SAMPLEISABOUTTENTIMESASHIGHASTHATFOR THE OTHER SAMPLES AND CORRESPONDS TO THE SIMULTANEOUS REDUCTION OF !U))) AND CERIA SURFACE SUPPORT AS ALREADY OBSERVED IN SEVERAL OTHER STUDIES EG 4HE HYDROGEN CONSUMPTIONMONITOREDFORTHE!U!L/CATALYSTSPREPARED BY!!AND)%ISOBSERVEDATHIGHERTEMPERATURE IEAND
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# RESPECTIVELY 4HE$05SAMPLESCONTAINVERYSMALLGOLDPARTICLESAFTER REDUCTIONUNDERHYDROGENAT#WITHALMOSTTHESAME SIZE ^ NM WHATEVER THE SUPPORT 4ABLE 4HE GOLD PARTICLE SIZE DOES NOT DEPEND ON THE GOLD LOADING WITHIN THERANGEOFLOADINGINVESTIGATED4ABLE )TCANBERECALLED THATVERYSMALLGOLDPARTICLESWEREALSOOBTAINEDONWT
4ABLE !U4I/AND!U!L/PREPAREDBYDIFFERENTMETHODSGOLDANDCHLORINECONTENTS GOLDPARTICLESIZEAFTERDIFFERENTTHERMALTREATMENTS ACTIVITYAND4/&AT #NDNOTDETERMINED
,OADINGWT !CTIVATION !U #L 'AS 4EMP#
#ATALYSTS
!U!L/$05UNWASHED
ND
(
!U4I/)%
!U!L/)%
!U!L/!!
!VERAGEGOLD PARTICLESIZENM !CTIVITYAT# !RITHMETIC 6OLUMIC MOLS G!U
4/&AT# S
MEAN
MEAN
(
(
(
STANDARDDEVIATION
0.6
SINGLE NARROW AND SYMMETRIC BAND AT CM WHICH TYPICALLY CORRESPONDS TO #/ ADSORBED ON LOW COORDINATION !U SITES OF METALLIC GOLD SURFACES 4HE )% CATALYST SHOWS A LOW INTENSE AND BROAD #/ BAND AT MUCH LOWER ENERGY CM )TMAYBEATTRIBUTEDTO#/ADSORBEDON NEGATIVELYCHARGEDGOLDCLUSTERSDUETOCHARGETRANSFER 4HE NEGATIVELY CHARGED GOLD SPECIES MAY ARISE FROM THE PRESENCEOFCHLORIDESEITHERONTHEALUMINASUPPORTCLOSETO THE PARTICLE OR MAYBE EVEN ON THE GOLD PARTICLE ITSELF AS REPORTED IN RECENT PAPERS ! SECOND BAND LESS INTENSEATCM MAYBEATTRIBUTEDTO#/ADSORBEDON POSITIVELY CHARGED !UD SPECIES OF ELECTRO DE½CIENT GOLD PARTICLES POSSIBLY MADE ELECTROPOSITIVE BY THE PROXIMITY OF OXYGEN "#ATALYTICRESULTS &IGUREINDICATESTHECONVERSIONOFBUTADIENEANDPROPENE ANDTHEFORMATIONOFTHEPRODUCTSASAFUNCTIONOFTEMPERATURE OVERA$05!U!L/CATALYST&IGURESHOWSTHATAT^# THE WHOLE BUTADIENE HAS BEEN CONVERTED INTO BUTENES WITHOUTFORMATIONOFBUTANELESSTHANPPM ANDWITHOUT SIGNI½CANT HYDROGENATION OF PROPENE TO PROPANE ^ PPM %VENAT# THEAMOUNTSOFBUTANEANDPROPANE FORMEDDONOTEXCEED^PPMAND^PPM RESPECTIVELY
(a)
0.5
2104
0.01
(b)/10 Log (lco/lref)
Hydrogen Consumption (a.u.)
!U4I/CATALYSTS 7HENTHE$05SAMPLESAREREDUCED ATHIGHERTEMPERATUREORARECALCINEDINAIR LARGERPARTICLE SIZES ARE OBTAINED 4ABLE 4HIS WAS ALSO PREVIOUSLY OBSERVED !SMENTIONEDIN3ECTION%XPERIMENTAL GOLD PARTICLESIZEONCERIACANNOTBEMEASUREDBY4%-4ABLE (OWEVER NODIFFRACTIONLINEOFMETALGOLDWASOBSERVEDBY 82$-OREOVER ACCORDINGTOAFORMER8!&3STUDYPERFORMED ON$05!U#E/SAMPLESOFALMOSTTHESAMEGOLDLOADING THEEXTENTOFTHECONTRACTIONOFTHE!U !UBONDLENGTHAND THE LOW !U !U COORDINATION NUMBER INDICATED THAT THE AVERAGEGOLDPARTICLESIZEWASLESSTHANNM /NECANNOTETHATWHENTHESAMPLESCONTAINCHLORIDES UNWASHED $05 ANDOR ARE PREPARED BY ANOTHER METHOD THAN $05 !! AND )% 4ABLE THE GOLD PARTICLES ARE LARGER FOR THE SAME CONDITIONS OF REDUCTION 2ATHER SMALL GOLD PARTICLES ARE NEVERTHELESS OBTAINED UNDER HYDROGEN WHICH IS NOT THE CASE WHEN A CALCINATION TREATMENT IS APPLIED #/ ADSORPTION MONITORED BY $2)&4 SPECTROSCOPY WAS PERFORMEDONTWO!U!L/SAMPLESAFTERINSITUREDUCTIONIN THE)2CELLUNDER(UPTO#ONESAMPLEPREPAREDBY $05GOLDPARTICLESIZE ^NM ANDONEBYIMPREGNATIONIN EXCESSOFSOLUTION)% GOLDPARTICLESIZE^NM &IGURE )N THECASEOFTHE$05SAMPLE #/ADSORPTIONAT24LEADSTOA
0.4 (e) (f)
0.3 0.2
2127
(d) (c)
0.1
2063
(a) (b)
0 0
100
200 300 400 Temperature (°C)
500
600
&IGURE 402PRO½LESOFAS PREPARED$05SAMPLESA !U4I/ B !U#E/ INTENSITYDIVIDEDBY C !U:R/ D !U!L/ANDOFAS PREPARED !U!L/PREPAREDBYE ANIONICADSORPTION!! ANDF IMPREGNATION WITHEXCESSOFSOLUTION)%
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2250 2200 2150 2100 2050 2000 1950 1900 Wavenumbers (cm-1)
&IGURE $2)&4SPECTRAUNDER#/(EAT24ON!U!L/PREPAREDBYA DEPO SITION PRECIPITATIONWITHUREA$05 ANDB IMPREGNATIONWITHEXCESSOF SOLUTION)% ACTIVATIONIN(AT#
2500 Butadiene 1-butene
2000 1500
cis-2-butene
1000
Propane
trans-2-butene
500
Butane
0 30
60
Butadiene and Alkanes Concentrations (ppm)
Butadiene, Butenes and Alkanes Concentrations (ppm)
3000
3000
Au/TiO2 Au/Al2O3 Au/ZrO2 Au/CeO2
2500 2000 1500 1000 500 0 30
90 120 150 180 210 240 270 300 Temperatures (°C)
60
90 120 150 180 210 240 270 300 Temperatures (°C)
&IGURE
4YPICALREACTIVITYOFAGOLDCATALYST$05!U!L/ ACTIVATIONIN(AT # WT!UAND PPM#L INSELECTIVEHYDROGENATIONOF BUTADIENEINTHEPRESENCEOFANEXCESSOFPROPENE%VOLUTIONOFTHE CONCENTRATIONSOFBUTADIENEANDPRODUCTSASAFUNCTIONOFTHEREACTION TEMPERATURE4HEOPENSYMBOLSCORRESPONDTOTHECONCENTRATIONSOF BUTADIENEATDECREASINGTEMPERATURE
%VOLUTIONOFTHEBUTADIENESOLIDLINES ANDALKANESDASHEDLINES CONCENTRATIONSASAFUNCTIONOFTHEREACTIONTEMPERATUREINSELECTIVE HYDROGENATIONOFBUTADIENEINTHEPRESENCEOFANEXCESSOF PROPENEFOR$05GOLDCATALYSTSSUPPORTEDONDIFFERENTSUPPORTS TITANIA; ALUMINA. ZIRCONIA8 ANDCERIA SEE4ABLE 4HEOPENSYMBOLSCORRESPONDTOTHECONCENTRATIONSOFBUTADIENEAT DECREASINGTEMPERATURE
WHICHISVERYLOWIFONECONSIDERSTHATTHEREISOFPROPENE IN THE GAS ¾OW /NE CAN ALSO NOTE THAT AT ^# AND AT # THEAMOUNTOFBUTANEPRODUCEDISABOUTTIMES AS LOW AS THAT OF PROPANE IE THE PROPANEBUTANE RATIO IS EQUAL TO THE PROPENEBUTENES RATIO 4HIS SUGGESTS THAT THE REACTIVITY OF PROPENE IS THE SAME AS BUTENES AND VALIDATES THECHOICEOFREPLACINGBUTENEBYPROPENESEE)NTRODUCTION 4HESAMETYPEOFCATALYTICBEHAVIOURWASOBTAINEDWITHALL THEGOLDCATALYSTSTESTEDINTHISWORK
&IGURE ALSO SHOWS THAT BUTENE IS THE MAIN PRODUCT AND THAT THE PERCENTAGES IN THE DIFFERENT BUTENES VARY AS FOLLOWS BUTENE CIS BUTENE TRANS BUTENE 4HEIR PROPORTIONSCHANGEWITHTEMPERATUREWITHASLIGHTDECREASE IN BUTENE AND AN INCREASE IN TRANS BUTENE MORE IMPORTANTTHANTHATOFCIS BUTENE INDICATINGISOMERISATION !LMOSTTHESAMEEVOLUTIONOFTHEPERCENTAGESIN THEDIFFERENTBUTENESASAFUNCTIONOFTHEREACTIONTEMPERATURE WAS OBSERVED WITH ALL THE GOLD CATALYSTS PRESENTED IN THIS STUDY THEREFOREFORTHESAKEOFCLARITY THEYARENOTREPORTED INTHEFOLLOWING½GURES 4HE CATALYTIC PROPERTIES OF GOLD SUPPORTED ON DIFFERENT OXIDES 4I/ !L/ :R/ AND #E/ WERE COMPARED 4HESE SAMPLES WERE PREPARED BY THE SAME $05 METHOD THEY CONTAIN WT !U AND NO DETECTABLE CHLORIDES AND THEIR GOLDPARTICLESIZEISALMOSTTHESAME ABOUTNM AFTERTHE SAMEACTIVATIONSTEPUNDER(AT#4ABLE &IGURE SHOWS THAT THE CURVES OF CONVERSION OF BUTADIENE VERSUS TEMPERATUREAREALMOSTSUPERIMPOSED EXCEPTMAYBEFOR!U #E/ WHICHSEEMSTOBESLIGHTLYMOREACTIVE BUTITSACTIVITY AT # IS ROUGHLY THE SAME AS THAT OF THE OTHER SAMPLES 4ABLE 4HE SELECTIVITIES TO BUTENES AND ALKANES ARE INDEPENDENT ON THE SUPPORT AND ARE THE SAME AS THOSE SHOWNIN&IGURE4ABLESHOWSTHATTHEACTIVITIESAND4/& ARERATHERSIMILARFORALLTHESAMPLES^MOLS G!U AND^ S RESPECTIVELY &IGUREALSOSHOWSDIFFERENCESINBUTADIENECONVERSIONS BETWEEN THOSE MEASURED AT INCREASING TEMPERATURE FULL SYMBOLS AND THOSE MEASURED AT DECREASING TEMPERATURE ISOLATED OPEN SYMBOLS INDICATING CATALYST DEACTIVATION 4HESEDIFFERENCESVARYFROMONECATALYSTTOANOTHERGOLDON TITANIA SHOWS THE HIGHEST DEACTIVATION WHILE GOLD ON CERIA SHOWSTHELOWEST(ENCE THENATUREOFTHESUPPORTSEEMSTO PLAYAROLEINCATALYSTDEACTIVATION4HISWILLBEDISCUSSEDINA FUTUREPAPER 4HE IN¾UENCE OF THE GOLD OXIDATION STATE WAS ALSO
Butadiene Concentrations (ppm)
Butadiene Concentrations (ppm)
&IGURE
3000
as prepared Au/Al2O3 “as prepared” as prepared Au/TiO2 “as prepared”
2500 (a) 2000 1500 1000 500
Au/Al2O3 reduced Au/TiO2 reduced
0 30
60
90 120 150 180 210 240 270 300 Temperatures (°C)
3000 2500
Au/CeO2 calcined as prepared Au/CeO2 “as prepared” Au/CeO2 reduced
(b)
2000 1500 1000 500 0 30
60
90 120 150 180 210 240 270 300 Temperatures (°C)
&IGURE %VOLUTIONOFTHEBUTADIENEFULLSYMBOLS ANDALKANESOPENSYMBOLS CONCENTRATIONSASAFUNCTIONOFTHEREACTIONTEMPERATUREINSELECTIVE HYDROGENATIONOFBUTADIENEINTHEPRESENCEOFANEXCESSOFPROPENEFOR A AS PREPAREDDASHEDLINES !U4I/8 !U!L/; ANDREDUCED SOLIDLINES !U4I/8 !U!L/; ANDB AS PREPARED. CALCINED 8 ANDREDUCED!U#E/; $05SAMPLES WT!U REDUCTIONIN( AT#ORCALCINATIONINAIRAT#
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INVESTIGATED4HEACTIVITYOFAS PREPAREDSAMPLES IECONTAINING THE!U)))SPECIESOFTHEDEPOSITEDPRECURSOR WASCOMPAREDTO CATALYSTS ACTIVATED UNDER ( IE CONTAINING METALLIC GOLD &IGURE SHOWS THAT THE THREE AS PREPARED !U4I/ !U#E/ AND!U!L/CATALYSTSARELESSACTIVETHANTHECATALYSTSACTIVATED UNDER()NSTEADOFSHOWINGANACTIVITYFROM^#ASINTHE CASE OF THE REDUCED SAMPLES THEY BECOME ACTIVE AT HIGHER TEMPERATURE AND # RESPECTIVELY 4HESE RESULTS COMBINEDTOTHERESULTSOF402 IETHETEMPERATURESATWHICH GOLDSTARTSREDUCING&IGURE ANDTOTHEFACTTHATTHEREACTANT ¾OW IS A REDUCING MIXTURE HYDROGEN AND ALKENES ARE AN INDICATIONTHATGOLDINITIALLYINTHEOXIDATIONSTATE)))ISNOTACTIVE ANDTHATITBECOMESACTIVEWHEN!U)))STARTSREDUCINGINTO!U UNDERTHEREACTANTSTREAM4HESAMPLECOLOURSAFTERREACTION IE DEEP VIOLET FOR !U4I/ DARK BROWN FOR !U#E/ PINK PURPLE FOR !U!L/ AREALSOANINDICATIONTHATGOLDREDUCES DURINGREACTION 4HE REQUIREMENT OF THE PRESENCE OF !U FOR AN ACTIVE CATALYST IS CON½RMED WITH THE EXPERIMENTS PERFORMED WITH !U#E/SAMPLE)THASBEENSHOWNTHATINCONTRASTTOOTHER SUPPORTSSUCHASALUMINAORTITANIA CERIASTABILISESGOLDINTHE OXIDATIONSTATE!U)))AFTERCALCINATIONUPTO# &IGURE BSHOWSTHAT!U#E/SAMPLECALCINEDAT#ISEVENLESS
Butadiene and Alkanes Concentrations (ppm)
3000 2500 2000 1500 1000 0.9 wt % Au 1.7 wt % Au 500 3.1 wt % Au 0 30 60 90 120 150 180 210 240 270 300 Temperatures (°C)
&IGURE
6 5 4 3 2 1 0 2.0
2.5
3.0 3.5 4.0 4.5 Average particle (nm)
6 5 4 3 2 1 0 5.0
TOF (10-3 s-1) per surface atom
Activity (μmol.s-1 .gAu-1)
%VOLUTIONOFTHEBUTADIENEFULLSYMBOLS ANDALKANESOPENSYMBOLS CONCENTRATIONSASAFUNCTIONOFTHEREACTIONTEMPERATUREINSELECTIVE HYDROGENATIONOFBUTADIENEINTHEPRESENCEOFANEXCESSOFPROPENEFOR $05!U!L/WITHDIFFERENTGOLDLOADINGSSEE4ABLE
&IGURE %VOLUTIONOFTHEACTIVITY8 AND4/&5 OF$05GOLDCATALYSTSSEVERAL BATCHESANDDIFFERENTACTIVATIONS SEE4ABLE INSELECTIVEHYDROGENA TIONOFBUTADIENEINTHEPRESENCEOFANEXCESSOFPROPENEAT#ASA FUNCTIONOFTHEAVERAGEGOLDPARTICLESIZEACTIVITYOFGOLDCATALYSTSPRE PAREDBYDIFFERENTMETHODSANDCONTAININGDIFFERENTLEVELSOFCHLORINE . ASAFUNCTIONOFTHEAVERAGEGOLDPARTICLESIZESEE4ABLE
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ACTIVETHANTHEAS PREPAREDSAMPLE 4HREE!U!L/CATALYSTSPREPAREDBYTHESAME$05METHOD ANDCONTAININGDIFFERENTGOLDLOADINGS ANDWT BUT THESAMEGOLDPARTICLESIZE4ABLE WERECOMPARED&IGURE SHOWSTHATTHECONVERSIONINCREASESWITHTHEGOLDLOADING AND THATTHEAMOUNTOFALKANESBUTANEANDPROPANE FORMEDIS ALSOPROPORTIONALTOTHEGOLDLOADING4HEACTIVITYAT#AND THE4/&AREHOWEVERNEARLYCONSTANT ANDDONOTDEPENDON THE GOLD LOADING 4ABLE 4HE SAME TYPE OF RESULTS WAS OBTAINEDWITH!U4I/CATALYSTS4ABLE 4HESELECTIVITIESTO BUTENESARENOTAFFECTEDBYCHANGESINGOLDLOADING !SSHOWNINFORMERPAPERS ITISPOSSIBLETOVARYTHE GOLDPARTICLESIZEINTHESAMPLESPREPAREDBY$05BYMODIFYING THE CONDITIONS OF ACTIVATION ! SET OF SAMPLES WITH DIFFERENT GOLDPARTICLESIZESWASOBTAINEDWITH$05SAMPLESSUBMITTED TO DIFFERENT ACTIVATION TREATMENTS AND ALSO ARISING FROM DIFFERENTBATCHES ORSUPPORTEDONDIFFERENTOXIDES &IGURESHOWSTHATTHEACTIVITYAT#SLIGHTLYDECREASES FROMTO MOLS G!U ASTHEGOLDPARTICLESIZEINCREASES FROMTONM WHILETHE4/&TENDSTOSLIGHTLYINCREASEFROM TO S &IGURE ALSO SHOWS THAT THE PREPARATION METHOD HAS A STRONGIN¾UENCEONTHEACTIVITYSINCETHESAMPLESPREPARED BY IMPREGNATION IN EXCESS OF SOLUTION )% AND ANIONIC ADSORPTION !! PROVIDE LESS ACTIVE CATALYSTS THAN THOSE PREPAREDBYDEPOSITION PRECIPITATIONWITHUREAFORTHESAME GOLDPARTICLESIZESANDSIZEDISTRIBUTION4ABLE 4HISISALSO THE CASE FOR THE UNWASHED $05 SAMPLE WHICH CONTAINS CHLORIDES AS DO THE )% AND !! SAMPLES 4HE SELECTIVITY IS ALSO SLIGHTLY AFFECTED SINCE ALTHOUGH BUTENE REMAINS THE MAINPRODUCT THEREISMOREISOMERISATIONINTRANS BUTENE 4HEIN¾UENCEOFPROPENECONCENTRATION AND ONTHEHYDROGENATIONOFBUTADIENE WASINVESTIGATED OVERA$05!U!L/CATALYSTWT &IGUREASHOWSTHAT THE BUTADIENE CONVERSION SLIGHTLY INCREASES AS PROPENE CONCENTRATIONDECREASES&ORINSTANCE THEACTIVITIESAT# ARE ANDMOLS G!U RESPECTIVELYFOR AND PROPENE4HECHANGEISNOTDRASTIC ANDTHEIN¾UENCEOF PROPENEISRATHERWEAKIFONEREMEMBERSTHATPROPENE CORRESPONDSTOACONCENTRATIONTIMESASHIGHASTHATOF BUTADIENE 4HEIN¾UENCEOFBUTADIENECONCENTRATIONAND ON THE HYDROGENATION OF PROPENE WAS ALSO INVESTIGATED OVERA$05!U!L/CATALYSTWT &IGUREBSHOWSTHAT PROPENE CONVERSION IS NOT AFFECTED BY THE PRESENCE OR THE ABSENCEOFBUTADIENE
$ISCUSSION !!CTIVITY /URRESULTSCON½RMTHATGOLDCATALYSTSAREACTIVEINREACTIONS OF HYDROGENATION BUT MUCH LESS THAN PALLADIUM 4HE GOLD ACTIVITY WAS AROUND MOLS G!U AT # 4ABLES WHEREASFOREXAMPLE THATOFPALLADIUMINHYDROGENATIONOF ACETYLENE IS ABOUT MOLS G0D AT # OR THAT OF
!G 0D!L/ CATALYST IS MOLS G0D AT # 4O INCREASETHEEF½CIENCYOFGOLDCATALYSTSTOSOMEEXTENT ITIS POSSIBLE HOWEVER TO INCREASE THE GOLD LOADING SINCE AS REPORTEDIN&IGUREAND4ABLE CONVERSIONISPROPORTIONAL TOTHEAMOUNTOFGOLD 4HEPOORCATALYTICACTIVITYOFGOLDCATALYSTSINHYDROGENATION COMPAREDTOTHATOF0DOR0TCATALYSTSISGENERALLYATTRIBUTED TO THE FACT THAT GOLD HARDLY DISSOCIATES MOLECULAR ( AS ESTABLISHED EXPERIMENTALLY AND THEORETICALLY (OWEVER SEVERAL AUTHORS HAVE OBSERVED THE DISSOCIATIVE CHEMISORPTIONOF($ ONGOLD½LMS/KADAETAL WHO STUDIEDTHEADSORPTIONANDREACTIONOFHYDROGENDEUTERIUM ONTHINGOLD½LMGROWNON)R NOTICEDTHAT( $ CAN DISSOCIATIVELYADSORBONTHESE!U½LMS4HEYATTRIBUTEDTHIS PROPERTY TO LOCALLY RELAXED SURFACE FEATURES LIKE DEFECTS /N THINGOLD½LMDEPOSITEDONPYREXGLASS 3TOBINSKI ETAL ALSO FOUND THAT ( CAN DISSOCIATIVELY CHEMISORB PROVIDING THATTHETHINGOLD½LMWASDEPOSITEDATLOWTEMPERATURE + ANDWASNOTSINTEREDAFTERWARDS4HEYCONCLUDEDTHAT( CHEMISORPTION OCCURRED ONLY ON SURFACE ATOMS OF LOW COORDINATIONNUMBER4HEN :ANELLAETAL PROPOSEDTHAT THE ACTIVITY OF GOLD CATALYSTS IN SELECTIVE HYDROGENATION OF CROTONALDEHYDEWASDETERMINEDBYTHEDISSOCIATIONSTEPOF MOLECULARHYDROGEN WHICHWASTHERATE LIMITINGSTEP-ORE RECENTLY COMBINED EXPERIMENTS OF 8!&3 ( CHEMISORPTION AND($EXCHANGEHAVEPROVENTHATHYDROGENDISSOCIATIVELY ADSORBSONTHEGOLDPARTICLESOF!U!L/CATALYSTSPREPARED BY IMPREGNATION AND DEPOSITION PRECIPITATION 4HE ADSORPTIONANDDISSOCIATIONOFHYDROGENWERELIMITEDTOTHE GOLDATOMSONCORNERANDEDGEPOSITIONS4HEAUTHORSALSO FOUNDTHATTHEHYDROGENDISSOCIATIONBYGOLDWASACTIVATED ANDTHATBOTHTHEACTIVITYIN($EXCHANGEANDTHEHYDROGEN UPTAKEINCREASEDWITHTEMPERATURE4HEYCONCLUDEDTHATTHE LOW HYDROGEN COVERAGE ON GOLD NANOPARTICLES IMPLIES THAT HYDROGENADSORPTIONDISSOCIATIONISTHERATE LIMITINGSTEPIN HYDROGENATIONREACTION 4HEEXPERIMENTSREPORTEDIN&IGUREANDCOMMENTEDON ABOVE PROVIDE A GOOD INDICATION THAT GOLD MUST BE IN THE METALLICSTATETOBEACTIVE ANDTHATWHENGOLDISINITIALLYIN CATIONIC FORM IT REDUCES UNDER THE REACTANT STREAM BEFORE REACHING#4HEFACTTHATGOLDMUSTBEMETALLICTOBE ACTIVEWASIMPLICITLYASSUMEDBYTHEAUTHORSWHOPUBLISHED PAPERS ON SELECTIVE HYDROGENATION OVER GOLD CATALYSTS PROBABLY BY COMPARISON WITH OTHER NOBLE METAL CATALYSTS (OWEVER TWORECENTPAPERSPUBLISHEDBY8UETAL ON BUTADIENEHYDROGENATIONOVER!U:R/CATALYSTSSEEMTO SHOWTHAT!U)))SPECIESWOULDLEADTOHIGHERACTIVITYTHAN!U &OR INSTANCE THE AUTHORS FOUND THAT FOR !U:R/ SAMPLES CALCINEDAT# THECONVERSIONOFAWT!USAMPLE CONTAININGMAINLY!U)))SPECIESWASHIGHERTHANTHATOFA WT!UCONTAININGABOUTOF!U)))AND!U%VENTHOUGH GOLDCOULDREDUCEDURINGTHEREACTIONPERFORMEDAT# THEGOLDOXIDATIONSTATEWASNOTCHARACTERISEDAFTERREACTION THISDOESNOTEXPLAINTHEDIFFERENCEOFCONVERSIONBETWEEN THETWOSAMPLES
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"3ELECTIVITY 4HE ADVANTAGE OF THE LOW HYDROGENATING ACTIVITY OF GOLD COMPARED TO PALLADIUM OR PLATINUM IS THAT GOLD IS VERY SELECTIVE AS ALREADY MENTIONED IN THE )NTRODUCTION 4HIS IS CON½RMEDBYTHERESULTSREPORTEDINTHISPAPER&ORINSTANCE &IGURESHOWSTHATTHEGOLDCATALYSTSAREVERYSELECTIVEFOR THE HYDROGENATION OF BUTADIENE INTO BUTENES EVEN IN THE PRESENCEOFANEXCESSOFPROPENETIMESHIGHER 5NDER OUREXPERIMENTALCONDITIONS ITISPOSSIBLETOTRANSFORM OF THE BUTADIENE INTO BUTENES WITH ONLY TRACES OF BUTANE FORMED PPM AT^# ANDONLY^PPMOFPROPENE HYDROGENATED %VEN AT HIGHER TEMPERATURE UP TO # THECONVERSIONOFPROPENEANDBUTENESINTOALKANESREMAINS VERY LOW ALTHOUGH IT GRADUALLY INCREASES WITH TEMPERATURE ^PPMOFPROPANEAT# IECONVERSION AND ^PPMOFBUTANE 4HESELECTIVITIESOBTAINEDWITHOURGOLDCATALYSTSAREMUCH HIGHER THAN THOSE OBTAINED WITH PALLADIUM CATALYSTS %VEN WITHBIMETALLIC0DCATALYSTS WHICHARESUPPOSEDTOBEMUCH MORE SELECTIVE THAN MONOMETALLIC 0D CATALYSTS SELECTIVITIES ARENOTASGOODASFORGOLDCATALYSTS&ORINSTANCE :HUETAL REPORTED THAT THE CONVERSION OF ETHYLENE INTO ETHANE OVERABIMETALLIC0D !GCATALYSTWASALREADYEQUALTOAT THE LOWEST TEMPERATURE FOR WHICH CONVERSION OF ACETYLENE WAS JUST REACHED ! FEW DEGREES ABOVE THIS TEMPERATURE SELECTIVITYDRASTICALLYDROPPED 4HE SLIGHTLY HIGHER ACTIVITY OF GOLD CATALYSTS IN HYDROGENATION OF BUTADIENE WHEN PROPENE WAS REMOVED FROMTHEREACTIONMIXTURE&IGURE INDICATESACOMPETITION OF ADSORPTION BETWEEN PROPENE AND BUTADIENE ANDOR HYDROGENONTHEGOLDSURFACESITES)TSEEMSTHATADSORBED PROPENE LIMITS THE ACCESS OF THE GOLD SITES TO THE OTHER REACTANTS (OWEVER PROPENE ADSORPTION IS PROBABLY WEAK OTHERWISEBUTADIENEHYDROGENATIONWOULDBEINHIBITED*IA ET AL COMPARED THE AMOUNT OF ALKENES AND ALKYNES ADSORBED AT # ON AN !U!L/ CATALYST AND FOUND MOLECULEOFACETYLENEADSORBEDPERSURFACEATOMOFGOLD ANDONLYMOLECULEOFETHYLENE IEARATIOOFABOUT BETWEENTHETWOMOLECULES)TCANBEANTICIPATEDTHATTHE RATIOISOFTHESAMEORDERFORBUTADIENEANDPROPENE !GAIN PALLADIUMBEHAVESMUCHDIFFERENTLY/VERPALLADIUM CATALYSTS THERATEOFHYDROGENATIONOFALKENESISHIGHERTHAN THATOFALKYNESORALKADIENES4HESELECTIVEHYDROGENATIONOF ACETYLENE CARRIED OUT BY *IA ET AL AND OF HYDROGENATION OF BUTADIENE PERFORMED BY 3ILVESTRE !LBERO ET AL BOTH OVER !U!L/ SHOW THE SAME FEATURES 4HE STRONGER ADSORPTIONONPALLADIUMOFACETYLENEBUTADIENETHANETHYLENE BUTENES INHIBITS THE ADSORPTION OF ALKENES AND THEREFORE THEIR HYDROGENATION WHICH RESULTS IN A HIGH SELECTIVITY TO PARTIALLY HYDROGENATED PRODUCTS )N CONTRAST IN THE ABSENCEOFACETYLENEBUTADIENE ETHYLENEBUTENESAREREADILY HYDROGENATED !S A CONSEQUENCE AS LONG AS ALKENES AND ALKYNESALKADIENESAREBOTHPRESENTONPALLADIUMSURFACES THE LATER ARE PREFERENTIALLY HYDROGENATED INTO ALKENES BUT WHEN ALMOST ALL THE ALKYNESALKADIENES ARE HYDROGENATED ALKENES CAN ADSORB AND REACT WITH A MUCH HIGHER RATE THAN THE
Butadiene and Alkanes concentrations (ppm) Propane concentrations (ppm)
CONCLUDED THAT THE TWO REACTIONS OF HYDROGENATION OF BUTADIENEANDOFALKENESAREBARELYRELATEDONETOTHEOTHER THEYTAKEPLACEINTWODIFFERENTRANGESOFTEMPERATURESLOW TEMPERATURE RANGE FOR BUTADIENE AND HIGHER TEMPERATURE RANGEFORPROPENE ANDTHEPRESENCEOFONETYPEOFMOLECULE ONLYSLIGHTLYIN¾UENCESTHEREACTIVITYOFTHEOTHER&IGURE
3000 2500 (a) 2000 1500 1000 30% propane 20% propane 500 0% propane 0 30 60 90 120 150 180 210 240 270 300 Temperatures (°C)
#"UTENEDISTRIBUTION 4HE SAME DISTRIBUTION OF BUTENES IE BUTENE CIS BUTENE TRANS BUTENE&IGURE WASOBTAINEDBY/KUMURA ETAL OVER!U!L/DURINGBUTADIENEHYDROGENATION IN( 4HEHIGHPROPORTIONOF BUTENEATLOWCONVERSIONISIN AGREEMENTWITHTHERESULTSOBTAINEDBY-OYES ETAL ON GOLD½LMSANDTHESEAUTHORSCORRELATEDTHISHIGHSELECTIVITYIN BUTENE TO THE HIGH 0AULING ELECTRONEGATIVITY OF METALLIC GOLD&IGURE WHICHREPORTSTHEEVOLUTIONOFTHEPERCENTAGES VERSUS REACTION TEMPERATURE SHOWS THAT THE PRODUCT DISTRIBUTION VARIES OVER THE WHOLE TEMPERATURE RANGE OF REACTION ANDTHATASTEMPERATUREINCREASES PARTOF BUTENE GRADUALLY TRANSFORMS MAINLY INTO TRANS BUTENE WHICH IS THERMODYNAMICALLYTHEMOSTSTABLEBUTENE4HEFACTTHATTHIS PHENOMENON OCCURS AT ANY TEMPERATURE AND THAT THE AMOUNTOFTRANS BUTENEGRADUALLYINCREASESASTEMPERATURE INCREASES IS AN INDICATION THAT THE CHANGE IN PRODUCT DISTRIBUTION RESULTS FROM ISOMERISATION OF BUTENE TO BUTENES4HISISCON½RMEDBYTHEFACTTHAT)NAMI ETAL WHO SPECI½CALLY STUDIED THE REACTION OF ISOMERISATION OVER UNSUPPORTEDGOLDMICRO SPHERES M OBSERVEDTHE ISOMERISATION OF BUTENE TO BUTENES UNDER HYDROGEN AT # /KUMURA ET AL ALSO REPORTED EXPERIMENTS INDICATINGTHAT BUTENEISOMERISESTO BUTENESIN(STREAM 4HIS PHENOMENON OF ISOMERISATION NOT ONLY INDICATES THAT ALKENE ADSORBS ON GOLD PARTICLES SPECI½C ADSORPTION MEASUREMENTSPERFORMEDBY*IAETAL ALSOPROVEDIT BUT ALSOSHOWSTHATGOLDISABLETOBREAK# (BONDS !GAIN THE BEHAVIOUR OF GOLD CATALYSTS IS DIFFERENT FROM THAT OF PALLADIUM 7ITH PALLADIUM BUTENE REMAINS THE MAIN PRODUCT AS LONG AS BUTADIENE CONVERSION HAS NOT REACHED 4HEN WHEN ALL THE BUTADIENE HAS REACTED
3000 2500
(b)
2000 1500 1000 500 0 30
without butadiene with butadiene 60
90 120 150 180 210 240 270 300 Temperatures (°C)
&IGURE %VOLUTIONOFTHEBUTADIENEFULLSYMBOLS ANDALKANESOPENSYMBOLS CONCENTRATIONSASAFUNCTIONOFTHEREACTIONTEMPERATUREFOR$05 !U!L/CATALYSTSINA BUTADIENEHYDROGENATIONASAFUNCTIONOF PROPENECONCENTRATION. ;5 AND8: B PROPENE HYDROGENATIONINTHEPRESENCE5 ORABSENCEOFBUTADIENE: ACTIVATIONIN(AT# WT!UAND PPM#L
REMAINING ALKYNESALKADIENES LEADING TO A COLLAPSE OF THE SELECTIVITY 4HE SELECTIVITY OF PALLADIUM CATALYSTS THEREFORE RESULTS FROM A COMPETITION OF ADSORPTION BETWEEN THE TWO TYPESOFMOLECULES )FGOLDCATALYSTSBEHAVEDONTHESAMEPRINCIPLE ONESHOULD OBSERVE THE FORMATION OF HIGH AMOUNTS OF ALKANES WHEN BUTADIENE IS ABSENT FROM THE REACTION MIXTURE (OWEVER ½GUREBSHOWSNODIFFERENCEINREACTIVITYOFPROPENEWHETHER BUTADIENE IS PRESENT OR ABSENT 6ICE VERSA THE ABSENCE OF PROPENEINTHEREACTIONMIXTUREDOESNOTDRASTICALLYIN¾UENCE THEHYDROGENATIONOFBUTADIENE ORSELECTIVITIES&IGUREA 4HISCLEARLYINDICATESTHATTHEREASONFORTHEHIGHSELECTIVITYOF GOLDISTOTALLYDIFFERENTFROMTHATOFPALLADIUM4HUS ITCANBE
Butenes proportion (%)
100 80 60 40
Cis-2-Butene Trans-2-Butene
20
Butene 0 30
60
90
120
150
180
210
240
270
300
Temperatures (°C)
&IGURE 0ROPORTIONINTHEDIFFERENTBUTENESPRODUCEDINSELECTIVEHYDROGENATIONOFBUTADIENEINTHEPRESENCEOFANEXCESSOFPROPENESAMEEXPERIMENTASIN &IGURE
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ISOMERISATION SUDDENLY OCCURS AND BUTENE TRANSFORMS TO TRANS BUTENE WHICHBECOMESTHEMAINBUTENE ANDTO CIS BUTENE 7ITH GOLD BUTENE IS ALWAYS THE MAIN PRODUCTINSPITEOFSLIGHTISOMERISATION.OTETHAT BUTENE IS THE MOST DESIRABLE PRODUCT FOR APPLICATION SEE )NTRODUCTION
WERESMALLERTHANOURS S INSTEADOF S AT# FORGOLDPARTICLESIZEAROUNDNM /NE CAN NOTE AGAIN THE DRASTIC DIFFERENCE WITH 0D!L/ CATALYSTS FORWHICHTHE4/&ALSOEXPRESSEDPERSURFACEATOM LINEARLY INCREASED BY A FACTOR OF FOR 0D PARTICLE SIZES INCREASINGFROMTONM
$2ELATIONBETWEENTHENATUREOFTHECATALYSTANDTHE CATALYTICACTIVITY
)N¾UENCE OF THE PREPARATION METHOD AND THE PRESENCE OF CHLORIDES 4HELOWERACTIVITYOFTHECATALYSTSCONTAININGCHLORINECOMPARED TOTHOSEWITHTHESAMEGOLDPARTICLESIZEBUTFREEOFCHLORINE &IGURE 4ABLE INDICATESTHATCHLORIDESINHIBITTHEREACTION ANDTHATITISIMPORTANTTOCONTROLTHEIRAMOUNTDEPOSITEDON THECATALYSTDURINGPREPARATION4HEISSUEOFTHEPRESENCEOF CHLORINE WHICH POISON THE GOLD CATALYSTS AND MUST BE ELIMINATED WASALSOREPORTEDBY/KUMURAETAL 4HEYFOUND THAT!U!L/CATALYSTPREPAREDBYIMPREGNATIONBECAMEMORE ACTIVE IN BUTADIENE HYDROGENATION IF AFTER CALCINATION PERFORMED TO REDUCE GOLD THE SAMPLE WAS WASHED IN HOT WATER WHICHREMOVEDCHLORINE 3EVERAL REASONS FOR THE INHIBITION OF THE REACTION WHEN CHLORINEISPRESENTINCATALYSTSCANBEANTICIPATED4HE$2)&43 #/ EXPERIMENTS PERFORMED ON !U!L/ SAMPLES CONTAINING CHLORINEORFREEOFCHLORINE REVEALDIFFERENCESINTHEFREQUENCIES OF #/ VIBRATION &IGURE 4HE MAIN #/ BAND AT LOW WAVENUMBERCM WHENTHESAMPLECONTAINSCHLORIDES &IGUREB ISANINDICATIONOFTHEPRESENCEOF!UD SPECIES)TIS POSSIBLE THAT THE !UD SPECIES HAS A LOWER ABILITY TO ADSORB UNSATURATEDMOLECULESANDORTODISSOCIATEHYDROGEN ANDAS ACONSEQUENCEISRESPONSIBLEFORLOWERCATALYTICACTIVITY)TIS ALSO POSSIBLE THAT THE !UD SPECIES STABILISE REACTION INTERMEDIATES SUCHASTHEHALFHYDROGENATEDALKENE LEADING TO A DECREASE OF THE FRACTION OF FREE GOLD SITES AND AS A CONSEQUENCE OF THE ACTIVITY 4HESE TWO REASONS MAY ALSO EXPLAINTHESMALLDIFFERENCEOFSELECTIVITY!THIRDEXPLANATION COULDBETHATIFCHLORIDESDIRECTLYINTERACTWITHGOLDSURFACE THEYWOULDINHIBITTHEACCESSTOTHEREACTANTS3OMERECENT PAPERSSHOWEDTHATHALIDESCANBEADSORBEDONMETALLICGOLD AND CAN SUPPRESS THE ADSORPTION OF REACTANTS ON THE PARTICLESSURFACE )NANYCASE THEPRESENCEOFCHLORINEIN SAMPLESMODI½ESTHEELECTRONICPROPERTIESOFGOLDASATTESTED BYTHE#/PROBE MOLECULE ANDLOWERSTHECATALYTICACTIVITY 7HERETHESECHLORINESPECIESARELOCATEDANDWHETHERTHERE IS A DIRECT RELATIONSHIP BETWEEN ELECTRONIC AND CATALYTIC PROPERTIESOFGOLDISSTILLAMATTEROFDISCUSSION
)N¾UENCEOFTHEOXIDESUPPORT /URRESULTSDONOTINDICATESIGNI½CANTIN¾UENCEOFTHENATURE OF THE OXIDE SUPPORT ON THE CATALYTIC PROPERTIES OF GOLD EXCEPTONDEACTIVATION WHICHWILLBEDISCUSSEDINAFUTURE PAPER &IGURE 4ABLE 4HISRESULTISNOTCONSISTENT WITH"UCHANANAND7EBB´S WHOSHOWEDTHATGOLDONG ALUMINA AND BOEHMITE WAS ACTIVE WHEREAS GOLD ON A ALUMINAANDSILICAWASINACTIVEINHYDROGENATIONOFBUTADIENE AT # .OTE THAT THESE SAMPLES WERE PREPARED BY IMPREGNATION WT OF !U AND EXHIBITED A BROAD DISTRIBUTION OF PARTICLE SIZES UP TO NM WITH THE LARGEST POPULATION OF SIZE IN THE NM RANGE /UR RESULTS ARE HOWEVER IN AGREEMENT WITH THOSE OF A MORE RECENT STUDY PERFORMED BY (ARUTA´S TEAM 4HEY DID NOT OBSERVE A SIGNI½CANTDIFFERENCEBETWEENGOLDCATALYSTSSUPPORTEDON ALUMINA SILICA OR TITANIA IN SELECTIVE HYDROGENATION OF BUTADIENE 4HE ABSENCE OF OXIDE SUPPORT EFFECT ON THE CATALYTIC ACTIVITY AND SELECTIVITY IS A GOOD INDICATION THAT THE HYDROGENATIONOFALKENESONLYOCCURSONTHEGOLDPARTICLES AND THAT THE SUPPORT DOES NOT DIRECTLY PARTICIPATE TO THE REACTION4HISISINCONTRASTWITHREACTIONSOFOXIDATION SUCH AS#/OXIDATION)NREACTIONSOFOXIDATION OXYGENACTIVATION POSSIBLY OCCURS ON THE OXIDE SUPPORTS WHEN THEY ARE REDUCIBLE OR AT THE GOLD SUPPORT INTERFACE )N CONTRAST INTHECASEOFHYDROGENATION ASMENTIONEDABOVE LOW COORDINATION SITES ON GOLD PARTICLES CAN DISSOCIATE ( 4HEREFORE A DIRECT INVOLVEMENT OF THE SUPPORT IS NOT REQUIRED ALTHOUGH THIS HYPOTHESIS WAS ONCE PROPOSED BY "UCHANANAND7EBB )N¾UENCEOFTHEGOLDPARTICLESIZE 4HEMODERATEEVOLUTIONOFACTIVITYAND4/&ASTEMPERATURE INCREASES&IGURE DEMONSTRATESTHATTHEGOLDPARTICLESSIZE HASNOTADRASTICIN¾UENCEONTHECATALYTICPROPERTIES)NDEED THE4/&INCREASESBYAFACTORWHENTHEPARTICLESIZEVARIES FROM TO NM 4HIS VARIATION IS SMALL COMPARED WITH THAT OBTAINED IN THE REACTION OF #/ OXIDATION FOR WHICH GOLD PARTICLESLARGERNMAREALMOSTINACTIVE ANDTHE4/&INCREASES BYAFACTOROF^ ANDACTIVITYPERGOFGOLDBYAFACTOR OF^ FORGOLDPARTICLESBETWEENANDNM4HESAME LIMITED VARIATION OF 4/& IN HYDROGENATION OF BUTADIENE WAS OBSERVEDBY/KUMURA ETAL FORTHESAMERANGEOFGOLD PARTICLESIZE4HEAUTHORSCONCLUDEDTHATTHEHYDROGENATION OFBUTADIENEWASNOTSTRUCTURE SENSITIVETOTHEPARTICLESIZE )TMAYBENOTEDTHATTHE4/&SDETERMINEDBYTHESEAUTHORS
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#ONCLUSION 4HIS STUDY ON THE SELECTIVE HYDROGENATION OF BUTADIENE IN THEPRESENCEOFANEXCESSOFPROPENECON½RMSTHEFORMER STUDIESPERFORMEDWITHALKADIENEALONETHATGOLDISHIGHLY SELECTIVE4HEPRESENCEOFALARGEAMOUNTOFALKENESDOES NOTDRASTICALLYMODIFYTHECATALYTICBEHAVIOUROFGOLD4HE MAIN REASON WHICH WAS INVESTIGATED IN THIS PAPER IS THAT EVEN THOUGH BUTADIENE ADSORBS SLIGHTLY MORE STRONGLY ON
GOLDTHANPROPENEASINTHECASEOFPALLADIUM THEREACTIVITY ISDRASTICALLYDIFFERENTFROMTHATONPALLADIUMSINCETHEREIS NO COMPETITION BETWEEN THE HYDROGENATION OF BUTADIENE INTOBUTENESANDTHEHYDROGENATIONOFBUTENESANDPROPENE INTOALKANES/VERGOLDCATALYSTS THESETWOHYDROGENATION REACTIONSOPERATEINTWOSEPARATETEMPERATURERANGES 4HE RESULTS SHOWED THAT THE METHOD OF DEPOSITION PRECIPITATIONWITHUREALEADSTOSMALLERGOLDPARTICLES ANDTO MOREACTIVECATALYSTSTHANANIONICADSORPTIONORIMPREGNATION -OREOVER EVEN FOR THE SAME GOLD PARTICLE SIZE DEPOSITION PRECIPITATION WITH UREA PROVIDES MORE EF½CIENT CATALYSTS IN SELECTIVE HYDROGENATION PROBABLY BECAUSE OF THE SMALLER CONCENTRATIONOFCHLORINEPRESENTINTHESAMPLES )T WAS ALSO FOUND THAT THE CATALYTIC BEHAVIOUR DOES NOT DEPEND ON THE NATURE OF THE SUPPORT PROVIDED THAT THE OTHERPARAMETERSAREIDENTICALSAMEPREPARATIONMETHODS GOLD LOADING AND GOLD PARTICLE SIZE )T DOES NOT DEPEND EITHERONTHEGOLDPARTICLESIZEATLEASTWITHINTHERANGEOF SIZE INVESTIGATED TO NM SINCE THE ESTIMATED 4/& IS ALMOSTCONSTANT
!NTOINE(UGONISA0H$STUDENTAT,23 (E IS NOW WRITING HIS THESIS ON SELECTIVE HYDROGENATIONOFDIENESOVERGOLD BASED CATALYSTS (IS THESIS WAS ½NANCIALLY SUPPORTED BOTH BY THE #.23 AND THE 7'# (E GRADUATED AS A CHEMICAL ENGINEER FROM %3#/- %COLE 3UPmRIEURE DE#HIMIE/RGANIQUEET-INmRALEIN WHEREHESTUDIED ORGANICCHEMISTRYANDCHEMICALENGINEERING
!CKNOWLEDGEMENTS
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4HE AUTHORS WANT TO THANK THE #.23 AND THE 7ORLD 'OLD #OUNCIL FOR THEIR ½NANCIAL SUPPORT TO !NTOINE (UGON´S 0H$GRANT
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